The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in engine timing applications as well as in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle. The invention also has applications with roller chains and chain-belts for continuously variable transmissions (CVT).
Conventional silent chains utilize links with inverted teeth for the transmission of power. Sets or rows of inverted tooth links are interleaved and connected by pins to form the chain assembly. Typically, guide links are press fit on the pins and are included along the outsides of both sides of the link rows to maintain the chain on the sprockets. The pins typically extend out beyond the edges of the guide links in the transverse direction of the chain, i.e., the direction transverse to the longitudinal movement of the chain around the sprockets.
As explained below, in one embodiment of the present invention, the pins are flush with the outside edges or sides of the outside links or guide links, or are constructed for minimal projection from the sides of the outside links. Minimization of the projection of the pins allows a narrower chain construction and permits embodiments where the guide links of the two chains in side-by-side relation may also be in touching relation.
The present invention has particular application to chain assemblies in which the chains and sprockets are offset, or phased, to modify the impact noise spectrum and chordal action noise spectrum. In a phased chain system, a single chain assembly is divided into, or replaced by, two side-by-side chains that are phased or offset by one-half pitch. In one embodiment of the present invention, the minimal pin projection is utilized on the sides of the two chains that are in the side-by-side relationship. The guide links with the minimal pin projection are placed in a groove in the center between the phased sprockets. With the guide links in the center groove, the guide links on the opposite or outer sides of the chains may be eliminated. Elimination of the guide links on one side of the chain, and running the guides links from the two chains in the center groove in a side-by-side and touching relationship, allows the achievement of a narrower phased chain system than in certain phased chain systems of the prior art.
As previously mentioned, silent chains are typically formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot members or pins, which are typically round pins or rocker joint pins received in a pair of apertures. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference.
Conventional silent chains typically include both guide links and inverted tooth links. The guide links are positioned on the outside edges of alternate sets of links. The guide links typically act only to position the chain laterally on the sprocket. Guide links do not mesh with the sprocket.
The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and sprocket. Each inverted tooth link includes a pair of apertures and a single depending tooth or a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined at a crotch. The inverted tooth links are designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links, or driving links, contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks. The contacts between the links and the sprocket teeth can be of the type which provide a power transfer, or can be of the nature of an incidental contact, or can include root contact or side contact.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts, Rotation of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket mounted on the camshaft. A chain for an engine timing drive application is shown in U.S. Pat. No. 4,758,210, which is incorporated herein by reference. Various types of engine timing systems and configurations are also shown in U.S. application Ser. No. 08/131,473, filed Oct. 4, 1993, now U.S. Pat. No. 5,427,580, which is incorporated herein by reference.
A second type of chain is known as "roller chain". A typical roller chain consists of alternate inner links and outer links. The inner links, which are also known as "bushing" links, Consist of spaced sidebars with bushings tightly received in openings, or apertures, at each end of the sidebars. The outer links, which are also known as "pin" links, consist of spaced sidebars with pins tightly received in openings, or apertures, at each end of the sidebars. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are provided on the bushings, and when the roller chain is wrapped about a sprocket, the teeth of the sprocket are received between the laterally spaced sidebars and the longitudinally spaced rollers. An example of roller chain is found in U.S. Pat. No. 4,186,617, which is incorporated herein by reference.
Roller chain drives can include both "true roller" and rollerless design. The true roller design includes the described rollers mounted about the bushings. Rollerless chain contains bushings that directly contact the sprocket. Both types of roller chain are typically specified in industry as British Standard chain and American National Standards Institute (ANSI) chain.
Noise is associated with chain drives. Noise is generated by a variety of sources, but in silent and roller chain drives it can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket and the mass of chain links contacting the sprocket at a particular moment or time increment.
Many efforts have been made to decrease the overall noise level and pitch frequency noise distribution in chain drives of the silent chain variety to minimize the objectionable effects of the pure sonic tones. Several of those efforts are discussed in the above-mentioned U.S. application Ser. No. 08/131,473, filed Oct. 4, 1993. The present invention finds application along with some of the noise reduction concepts discussed in the above-mentioned application, including randomization and phasing of the chain assemblies. However, the present invention has broader applications to chain systems that include, for example, non-phased sprockets or non-randomization of link profiles.
Phasing the chain and sprocket relationship can reduce the number of chain link teeth (or mass) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket. The chain randomization and sprocket phasing modifications can alter the impact and chordal action generated sound patterns.
However, in the narrow chain assembly package requirements that are particularly found in modern engine timing systems, the use of a phased chain system can be difficult in that the single chain is often replaced by two chains that are placed in side-by-side and phased relation. The need to place two phased chains in side-by-side relationship in the same width previously occupied by a single chain requires elimination of inside links or use of thinner inside links. (The term "inside link" or "inner link" is used to describe an articulating link, or link that articulates with respect to the pins, with teeth constructed to,drive the sprocket, in contrast to conventional "guide links" that are press fit and act to maintain the chain on the sprocket.) Such a modification is disadvantageous in that it requires fewer inner links across the width of the chain, or thinner inner links across the chain, which generally result in a weaker chain assembly than the assembly with a greater number of inner links across the width of the chain.
Modern engine timing systems often have as few as four links in the non-guide row and four or five links in the guide row. (The term "guide row" refers to the rows or sets of links along the length of the chain that include guide links on the outsides, while the term "non-guide row" refers to the rows along the length of the chain that are interleaved with the guide rows and do not include guide links on the outside.) In order to package such a narrow timing system in a phased system in approximately the same width, without decreasing the link thickness, the chain system often requires the use of chains laced with as few as two links in the guide row and two links in the non-guide row, i.e., what is referred to as a "2.times.2 lacing."
Silent chains typically utilize two conventional guide links, i.e., guide links without inverted teeth that are designed to contact the sprocket and provide a driving force, in each guide row. In a 2.times.2 lacing, such a construction results in every guide row, i.e., every other row of the chain, not having a driving contact with the sprocket. Such a construction that fails to provide a driving or power transmission contact with the sprocket in every row can result in a noisier chain than a chain in which every row has a driving contact with the sprocket.
Moreover, phased chain systems as well as side-by-side non-phased chain systems, are conventionally constructed with the two chains in a spaced-apart relationship. The spacing is provided between the two chains to assure that the chains do not contact one another during operation. In high speed automotive applications, significant movement occurs in the portions of each chain that span the longitudinal space between the driving and driven sprockets of each assembly. The separation between the two chains in the transverse direction is provided to prevent any contact between the two chains during such movement. Clearances between the chain and other structures are typically recommended in order to avoid contact from longitudinal or transverse movement of the chain during operation. The separation distance between the chains also contributes to the size or overall width of the chain package.
The present invention is directed to overcoming such disadvantages. The present invention provides other advantages in decreasing the width of the package size of the phased chains or allowing more inner links in a chain of the same width as without the present invention.